Sex-related and stage-dependent source-to-sink transition in Populus cathayana grown at elevated CO2 and elevated temperature

Dioecious plants, which comprise more than 14,620 species, account for an important component of terrestrial ecosystems. Hence, understanding the sexually dimorphic responses in balancing carbon (C) supply and demand under elevated CO2 is important for understanding leaf sink-to-source transitions. Here we investigate sex-related responses of the dioecious Populus cathayana Rehd. to elevated CO2 and elevated temperature. The plants were grown in environmentally controlled growth chambers at two CO2 enrichment regimes (350 +/- 20 and 700 +/- 20 mu mol mol(-1)) with two temperature levels, elevated by 0 and 2 +/- 0.2 degrees C (compared with the out-of-chamber environment). Plant growth characteristics, carbohydrate accumulation, C and nitrogen (N) allocation, photosynthetic capacity, N use efficiency and the morphology of mesophyll cells were investigated in the developing leaves (DLs) and expanded leaves (ELs) of both males and females. Elevated CO2 enhanced plant growth and photosynthetic capacity in DLs of both males and females, and induced the male ELs to have a greater leaf mass production, net photosynthesis rate (P-n), chlorophyll a/b ratio (Chl a/b), soluble protein level (SP), photosynthetic N use efficiency and soluble sugar level compared with females at the same leaf stage. Elevated temperature enhanced source activities and N uptake status during CO2 enrichment, and the combined treatment induced males to be more responsive than females in sink capacities, especially in ELs, probably due to greater N acquisition from other plant parts. Our findings showed that elevated CO2 increases the sink capacities of P. cathayana seedlings, and elevated temperature enhances the stimulation effect of elevated CO2 on plant growth. Male ELs were found to play an important role in N acquisition from roots and stems under decreasing N in total leaves under elevated CO2. Knowledge of the sex-specific leaf adaptability to warming climate can help us to understand sex-related source-to-sink transitions in dioecious plant species.